Which way will the pepper raft go?
Pepper can float as if water wears an invisible skin. What if soap touches only one side? Find which way the raft moves first.
A springy top can carry a rider
Clean water has a springy top. Neighboring water bits tug one another, so the surface can support pepper—and even a water strider.
Press the clean surface
Push the practice surface. Its connected pulls share the load like a tiny trampoline.
Soap weakens one patch
Add soap to the center of this practice patch. Nearby links fade while distant links stay strong.
A sheet follows the stronger tug
Change two generic pulls. The ribbon travels toward whichever hand pulls its shared sheet more strongly.
Now move the soap to the left
New dish: the pepper raft starts in the center. Soap waits at the LEFT edge; the rest stays clean.
still start · equal surface pulls · no motion trail
Commit before the new setup runs.
Soap touches the LEFT side. Which way will the pepper raft move first?
Spread the soap patch and watch the whole top layer.
